Issue 49

E. Abdelouahed et alii, Frattura ed Integrità Strutturale, 49 (2019) 690-697; DOI: 10.3221/IGF-ESIS.49.62

25

Pipeline Steel API 5L X70 , e pipe

= 4 mm

=2 mm

Composite Patch, e patch Adhesive FM-73, e a Crack length a=5mm

= 0.2 mm

20

K 1 (MPa.m 0.5 ) 10 15

5

Boron/epoxy Carbon/epoxy Glass/epoxy

0

20

40

60

80

100

120

depth crack

(%)

Figure 6 : Variation of SIF as a function of the crack depth of the pipeline

Effect of the thickness of the patch Fig. 7 shows the evolution of the stress intensity factor at the crack front of the repaired steel pipe API 5L X70 as a function of the thickness variation of the composite part independently of the boron/epoxy, the glass/epoxy or carbon/epoxy. We note that the K I decreases as the thickness of the patch increases in the three different cases of repair and the smallest value is when the thickness of the patch is equal to the thickness of the pipeline.

6.4

Pipeline Steel API 5L X70 , e pipe

= 4 mm

Composite Patch, e patch Adhesive FM 73, e a

=Variable

6.3

= 0.2 mm Crack length a=5mm

6.2

6.1

K 1 (MPa.m 0.5) 5.9 6.0

5.8

Boron/epoxy Carbon/epoxy Glass/epoxy

5.7

5.6

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

e patch

Figure 7 : SIF variation according to composite patch thickness

Likewise, the reduction of the stress intensity factor follows the same variation as a function of the thickness of the patch, and always keeps the advantage of its quality (boron, carbon, glass) between them. The more the patch increases in thickness, the greater the charge transfer by the adhesive. This considerably reduces the SIF, but remains conditioned by the strength of the adhesive. Effect of change in crack length Fig. 8 shows the variation of the stress intensity factor at the crack front in a pipeline repaired by three different types of composite patches (boron/epoxy, glass/epoxy and carbon/epoxy) as a function of the length of the crack. From this Fig. 5, we notice that the development of the crack gives us larger values of K I , which means that the quality of the repair by composite patches decreases. We also note that the most effective material for repair in case of long cracks is boron/epoxy. Reducing the stress intensity factor is always possible with a more rigid composite choice but it is clearly

695